He tells us how to install from a Ubuntu/Mint[DEB] distro, then how to install from a Suse/Fedora/[RPM] distro. Fair enough.

But then he says "where you have two .. distros installed, try switching from the one controlling Grub to the other"

Why? Once Grub 2 is installed it can boot either surely, it does not need to be "controlled" by the one you want to boot. Why does he go through a palava of "switching control" from Suse to Mint and then back again? Am I missing something here or is this just for fun ?

I also have a problem with the very concept of Grub being "controlled" by any one distro. I think/thought a boot manager should be OS neutral, especially if it is in the MBR. While, clearly, Grub needs to be installed by one distro or another, after that it should be independent surely?

FWIW, my boot manager is Smart Boot Manager [SBM] in the MBR, and it is this neutral SBM that gives me my choice of OS. To boot a Linux distro it hands over to a Grub [1] in the Boot Sector of that distro's partition which immediately boots it. So I have several Grubs (and a Windows bootloader - and a DOS bootloader believe it or not) around my drives. Come to think of it, those Grubs do have graphical backgrounds appropriate to that distro but I do not mind that because they are exclusively for that distro and in its partition.

Unsolved mysteries of the Universe, No 13 :-
How many remakes of Anna Karenina does the World need?

He tells us how to install from a Ubuntu/Mint[DEB] distro, then how to install from a Suse/Fedora/[RPM] distro. Fair enough.

But then he says "where you have two .. distros installed, try switching from the one controlling Grub to the other"

Why? Once Grub 2 is installed it can boot either surely, it does not need to be "controlled" by the one you want to boot. Why does he go through a palava of "switching control" from Suse to Mint and then back again? Am I missing something here or is this just for fun ?

I also have a problem with the very concept of Grub being "controlled" by any one distro. I think/thought a boot manager should be OS neutral, especially if it is in the MBR. While, clearly, Grub needs to be installed by one distro or another, after that it should be independent surely?

FWIW, my boot manager is Smart Boot Manager [SBM] in the MBR, and it is this neutral SBM that gives me my choice of OS. To boot a Linux distro it hands over to a Grub [1] in the Boot Sector of that distro's partition which immediately boots it. So I have several Grubs (and a Windows bootloader - and a DOS bootloader believe it or not) around my drives. Come to think of it, those Grubs do have graphical backgrounds appropriate to that distro but I do not mind that because they are exclusively for that distro and in its partition.

FYI I wrote that

It's just a project.

You are correct that once grub is installed by say Ubuntu it will boot Ubuntu and any other OS's installed (Linux or Windows), that's the idea any way. In practice, it doesn't always work out that way.

You ask why all the switching?It's just to illustrate the practice. You would be surprised how often we get people asking in the forums..."I just installed Ubuntu to try it.. but I want my XXXX grub back, it's way prettier than Ubuntu's" ORA user test another distro, planning to use it, but finds it doesn't meet up to expectations, he may want to switch grub back to his other distro etc..

I also have a problem with the very concept of Grub being "controlled" by any one distro. I think/thought a boot manager should be OS neutral, especially if it is in the MBR.

Unfortunately it doesn't work that way - at least not at a standard user level. But it is true, technically you can edit any grub menu at boot to do whatever you edit in, assuming the boot option exists and you edit it in correctly, it will boot.

But when a distro is installed and allowed to write grub, as a generalization, it does take control of booting/grub.